Operation voltage auto-adjustable active matrix organic light emitting diode circuit and auto-adjusting method thereof
An operation voltage auto-adjustable circuit for active matrix organic light emitting diode (“AMOLED”) and an auto-adjusting method thereof is provided. The circuit for automatically adjusting a operation voltage of an AMOLED includes a display panel of an AMOLED having a terminal of an organic light emitting diode (“OLED”); and an auto-adjusting circuit connected to the terminal of the OLED, wherein a current passing through the terminal of the OLED is detected by the auto-adjusting circuit, and a voltage applied to the terminal of the OLED is adjusted by the auto-adjusting circuit according to the current detected. Therefore the current passing through the terminal of the OLED is sensed to automatically adjust the voltage applied thereto, and the current passing through the terminal of the OLED is stably maintained.
Latest Au Optronics Corporation Patents:
This application claims the priority benefit of Taiwan application serial no. 92105112, filed on Mar. 10, 2003.
BACKGROUND OF INVENTION1. Field of the Invention
The invention generally relates to an active matrix organic light emitting diode (“AMOLED”) circuit. More particularly, the present invention relates to an operation voltage auto-adjustable AMOLED circuit and auto-adjusting method thereof.
2. Description of the Related Art
With the advancement of communications technology, devices such as computers, workstations, mobile phones, personal digital assistants (PDA), and digital cameras are improved on a daily basis. A display device is essential in each of the devices. In recent years, flat panel display (FPD) is commonly used because of its limited dimension, lightweight, and electricity saving features.
Among varieties of FPD, since active matrix organic light emitting diode (AMOLED) possesses a wider viewing angle, good color contrast, lightweight, thinner structure, high response speed and low cost, thus AMOLED is applicable to portable image devices such as notebooks, PDAs and mobile phones, and especially can be used in large size displays such as televisions and monitors.
However, as in the diagram shown in
Id=(½)k(Vgs−Vth)(Vgs−Vth) (1)
Therefore, the current Id passing through an OLED will decrease as the threshold voltage Vth of the TFT increases, the performance of the brightness of the OLED is reduced, and thus the lifetime of the device is reduced.
SUMMARY OF INVENTIONAccordingly, the purpose of the present invention is to provide an operation voltage auto-adjustable AMOLED circuit and auto-adjusting method thereof, in which the current passing through the terminal of the OLED is sensed to automatically adjust the voltage applied thereto. Therefore the current passing through the terminal of the OLED is stably maintained.
In order to achieve the above objects and other advantages of the present invention, an embodiment of an operation voltage auto-adjustable AMOLED circuit is provided. The circuit for automatically adjusting an operation voltage of an active matrix organic light emitting diode includes a display panel of an AMOLED having a terminal of an OLED; and an auto-adjusting circuit connected to the terminal of the OLED, in which a current passing through the terminal of the OLED is detected by the auto-adjusting circuit, and a voltage apply to the terminal of the OLED is adjusted by the auto-adjusting circuit according to the current detected. Therefore the current passing through the terminal of the OLED is stably maintained.
In a preferred embodiment of the present invention, the auto-adjusting circuit includes a resistor, a subtracting circuit, a comparing circuit and a digital processor. The resistor is provided for generating a sensing voltage according to the detected current of the terminal of the OLED. The subtracting circuit connected to the resistor is provided for computing a voltage difference between the sensing voltage and the voltage applied to the terminal of the OLED. The comparing circuit is provided for comparing the voltage difference with a reference voltage in order to provide a control signal. And the digital processor connected to the comparing circuit is provided for automatically adjusting the voltage applied to the terminal of the OLED according to the control signal.
In an embodiment of the present invention, the resistance of the resistor is less than about 10 ohm.
In an embodiment of the present invention, the reference voltage is computed according to a standard value of the current passing through the terminal of the OLED.
Another embodiment of the present invention of a method for automatically adjusting an operation voltage of an AMOLED is provided. The method includes sensing the current of the terminal of a OLED; and adjusting the voltage applied to the terminal of the OLED according to the sensed current of the terminal of the OLED automatically. Therefore the current passing through the terminal of the OLED is stably maintained.
Accordingly, when the operation voltage auto-adjustable AMOLED circuit and auto-adjusting method thereof described in the embodiment of the present invention is provided, the current passing through the terminal of the OLED is sensed to automatically adjust the voltage applied thereto, and the current passing through the terminal of the OLED is stably maintained.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. Moreover, each embodiment described and illustrated herein includes its complementary conductivity type embodiment as well.
As described above, the brightness of the OLED 240a is proportional to the current Id passing through the OLED 240a, and the current Id can be described by equation (1). When the scan line of the pixel is activated, the first TFT 210a is turned on in order to transmit the voltage of the data line to the gate of the second TFT 220a, and a gate voltage Vg of the second TFT 220a is achieved. If the voltage across the OLED 240a is Voled, then the voltage Vgs between the gate and the source of the second TFT 220a will become: Vgs=Vg Vs=Vg (Vss+Voled)
Because of the threshold voltage Vth of the second TFT 220a is known, according to the equation (1), the voltage value of the data line can be decided according to the brightness required.
However, referring to
Referring to
In order to reduce the effect of the resistor 320 to the driving circuit, the resistance of the resistor 320 should be as low as possible. For example, the resistance of the resistor is less than about 10 ohm. As to the reference voltage Vref, the reference voltage Vref is computed according to a standard value of the current passing through the terminal 311 of the OLED. And the voltage Vss applied to the terminal 311 of the OLED is adjusted according to the sensed circuit of the terminal 311 in order to maintain the stability of the current passing through the terminal 311 of the OLED.
Likewise,
According to the embodiment described above of the present invention, a method for automatically adjusting an operation voltage of an AMOLED is provided. The method includes sensing a current of the terminal of an OLED; and adjusting a voltage applied to the terminal of the OLED according to the sensed current of the terminal of the OLED automatically. Therefore the current passing through the terminal of the OLED is stably maintained.
Accordingly, when the operation voltage auto-adjustable AMOLED circuit and auto-adjusting method thereof described in the embodiment of the present invention is provided, the current passing through the terminal of the OLED is automatically adjusted and stably maintained. Moreover, the lifetime of the devices can also be extended.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
Claims
1. A circuit for automatically adjusting an operation voltage of an active matrix organic light emitting diode (“AMOLED”), comprising:
- a display panel of an AMOLED having a cathode terminal of an organic light emitting diode (“OLED”); and
- an auto-adjusting circuit connected to the cathode terminal of the OLED, wherein a current passing through the cathode terminal of the OLLED is detected by the auto-adjusting circuit, and a voltage applied to the cathode terminal of the OLED is adjusted by the auto-adjusting circuit according to the current detected.
2. The circuit of claim 1, wherein the auto-adjusting circuit comprising:
- a resistor for generating a sensing voltage, wherein the sensing voltage is generated according to the detected current of the cathode terminal of the OLED;
- a subtracting circuit connected to the resistor for computing a voltage difference between the sensing voltage and the voltage applied to the cathode terminal of the OLED;
- a comparing circuit for comparing the voltage difference with a reference voltage in order to provide a control signal; and
- a digital processor connected to the comparing circuit for automatically adjusting the voltage applied to the cathode terminal of the OLED according to the control signal.
3. The circuit of claim 2, wherein the resistance of the resistor is less than about 10 ohm.
4. The circuit of claim 2, wherein the reference voltage is computed according to a standard value of the current passing through the cathode terminal of the OLED.
5. A method for automatically adjusting an operation voltage of an active matrix organic light emitting diode (“AMOLED”), comprising:
- sensing a current of the cathode terminal of a OLED; and
- adjusting a voltage applied to the cathode terminal of the OLED according to the sensed current of the cathode terminal of the OLED automatically.
6778151 | August 17, 2004 | Li |
20020030647 | March 14, 2002 | Hack et al. |
20030020413 | January 30, 2003 | Oomura |
20030095087 | May 22, 2003 | Libsch et al. |
20030155866 | August 21, 2003 | Iwata et al. |
20040051690 | March 18, 2004 | Chang |
Type: Grant
Filed: Aug 21, 2003
Date of Patent: Aug 23, 2005
Patent Publication Number: 20040178740
Assignee: Au Optronics Corporation (Hsinchu)
Inventors: Yi-Chen Chang (Taipei), Shuohsiu Hu (Tainan)
Primary Examiner: Tuyet Thi Vo
Attorney: Jiang Chyun IP office
Application Number: 10/604,839